Disabled check of upstream version.

Removed pretest hook that was failing the build when our npm fork was behind
the latest npm version shipped in node v0.10.

- The hook was run only after a change was pushed. We need to run it
  periodically. To keep Amazon EC2 fees low, it's probably better to run
  the check as a standalone job that does not run teh full test suite.

- We need to figure out what's the best way to merge upstream changes after
  the npm's license changed to Artistic 2.0.